Most lead-based perovskite compounds yield high dielectric constant, e.g., εr>2000, which is the requirement for small capacitors in microelectronic industry. An advantage of the lead-based materials is low sintering temperature, which is typically below 1200° C. Since these lead-based ceramics have a wide range of Curie temperatures, a multilayer ceramic capacitor can be fabricated in different layers to meet the required temperature by integrating the overall properties of the multilayer.
Most of the dielectric ceramic compositions consist of three or more different lead-based or non-lead ceramics. In addition, in many cases, small amounts of some other elements are required to modify the main solid solution. Lead magnesium niobate Pb(Mg1/3Nb2/3)O3, lead nickel niobate Pb(Ni1/3Nb2/3)O3, lead zirconate PbZrO3 and lead titanate PbTiO3 are widely used as dielectric ceramic compositions. These materials and their solid solutions can give high dielectric constants (εr>10000) but the disadvantage is large fluctuations in the dielectric constant with increasing or decreasing temperature. Most applications of these materials are therefore concentrated on the utilization of their dielectric constants at a specific temperature. For example, lead magnesium niobate, lead nickel niobate and lead titanate, which are mentioned in the U.S. Pat. No. 5,275,988. The addition of strontium, barium and calcium ions to ternary ceramics replaces some of the Pb ions, enabling modification of the dielectric and temperature properties. The modified ternary ceramic systems exhibit high dielectric constants (εr>10000) and satisfying the Y5U characteristics (−30° C. to 85° C., ΔC/C (25° C.), +22% to −56%). In U.S. Pat. No. 5,633,215, the main components of the dielectric composition consist of lead magnesium tungstate (Pb(Mg1/2W1/2)O3), lead zirconate and lead titanate and at least one rare-earth oxide additive. The dielectric constants of these compositions vary from 1600 to 6800 but the variations in the dielectric constant at −30° C. and 85° C. are large. Typical variations are about 15% or more. Another U.S. Pat. No. 5,861,350 claims reasonably high dielectric constant (˜4000 to 10000) but the temperature stability falls within ±30%.